Articles

20060919 The Wait Is Over- Understanding Latency and DSM

The Wait Is Over

Spektrum 2.4GHz modules and radio gear have become some of the most innovative products to be introduced in RC in quite some time. Racers and hobbyists around the world have adopted this breakthrough technology at an amazing rate. From the time that the original modules were made available to the general public, the response has been largely positive, highlighted with the RC Innovation of the Year Award from Radio Controlled Car Action Magazine. Like any new technology though, there have been some questions about the performance— namely the latency of a DSM signal vs. a standard FM or PCM signal.

Understanding Latency and DSM

Latency is the delay that occurs from the moment an input is given at the transmitter (steering or throttle movement) to the moment that the servo receives a pulse telling it to move. Most crystal-based radio systems have a latency between 10–20 milliseconds. That’s only .0010–.0020 of a second of latency.

Spektrum’s first DSM system added an additional 5.6m/s of latency into the total system latency of a radio and its module. Again, we’re speaking in terms of thousandths of a second here. While drivers around the country used the original system and loved them, there were some who said they could feel the additional latency in the system and felt it was hampering their performance.

Listening to the Racers: The Pro Series is Born

As we’ve shown, 5.6m/s isn’t much. Still, some racers insisted they could feel a slower reaction time when they equipped their radios with Spektrum modules. In some instances, the latency could be compensated for by either turning up throttle or steering exponential rates or by using faster servos; others simply couldn’t make the adjustment. Spektrum engineers immediately when to work to improve transmission time while still maintaining a solid RF link for that locked-in feel. Through testing and development with engineers and top racers such as Travis

Amezcua, E.J. Evans, John Adams, and Sonny Brown, it became possible to drop the latency to only 3m/s while still maintaining a robust RF link. And so, the Pro Series Spektrum equipment was born.

While they were at it, they incorporated a few other changes to the Pro Series equipment. One included a new conformal coating to the circuit boards inside the receivers to make them waterproof. Another was the new opaque receiver case that is fuel proof, and which improves durability and reliability, especially in larger 1/8-scale nitro vehicles. The Pro Series receivers also feature improved firmware that prevents ESD (electro-static discharge) issues from the get-go.

What about ESD???

Some racers experienced something that did not crop up in initial product testing: an electro-static discharge (ESD) issue. Most of the initial testing on Spektrum Modules and receivers were done on asphalt, but once the indoor carpet season began, some ran into issues where the fail-safe on the receiver would kick in, essentially shutting the car down. Between several testers, it was found that a firmware upgrade to the receiver would eliminate the ESD issues. Additionally, it was discovered that the routing of the transmitter’s antenna wire inside the module case placed the wire directly over the power capacitors. There were times when this placement of the antenna lead could cause a driver to experience glitching issues. Again, Spektrum Engineers came up with a fix that was easy and effective. A new antenna was designed with a longer lead on it that allowed the wire to be routed around the side of the RF board instead of over it. All the standard and Pro Series modules and receivers shipping now feature all of the firmware and antenna updates. Additionally, those who already purchased Spektrum systems before May of 2006 can simply send in their system for the firmware and antenna updates to be made free of charge.

From the mouths of the racers

The ultimate test of any product is how it performs in the hands of the end users, not the engineers. We’ve talked with a number of racers recently to get their take on Spektrum latency since the introduction of the Pro Series.

I started using the original Spektrum system at the Reedy Truck race in 2004 when it was still in the prototype stages. During the past 2 years, I have used Spektrum modules and receivers and spent many hours track-testing the system with one of our designers, Mathew Lee. From the first day I started using Spektrum to today, I've only gone back to a normal crystal-based radio system once. I did this as an experiment and to simply try it out again.

When I did, boy did I have a bunch of glitching problems. Since that last test, I will never go back to crystals again. With the release of the super-tiny SR3500 micro receiver, it’s now the only receiver I use, and I run it in every car that I race. From 1/8 gas off-road to 1/10 electric off-road, the new SR3500 is bulletproof, both in terms of durability and signal quality. Since I have upgraded my radio to Spektrum 2.4GHz DSM equipment, I've never once had any kind of a radio problem. And for those who think that Spektrum slows you down, I have won more than a few National Championships with Spektrum equipment in my cars. The proof is in the results.

Todd Hodge—Team Manager, Team Losi

I was lucky enough to be one of the first testers for the Spektrum equipment. I felt it was the greatest and most innovative idea for an RC product that had ever been designed. As we headed into the carpet season with our touring cars, we felt that there were some potential problems with the latency. We changed back to our crystal-based equipment soon after that.

Recently, however, I was introduced to the new Spektrum Pro Series modules and the new Spektrum SR3500 Micro Receiver. While attending the IFMAR Touring Car World Championships in Italy, I was experiencing major glitching problems and needed a fix fast. I installed the new Spektrum Pro Series Module in my JR Z-1 and SR3500 Micro Receiver in my Team Losi JRX-S Type R touring car and never looked back. It was awesome. I never experienced another problem the rest of the weekend. Back in the States, I have continued to use the Spektrum Pro Series on carpet and found that it works flawlessly. It has no latency issues that I can feel. I will be running the entire season with the new Spektrum Pro Series equipment to ensure the proven preciseness that has been incorporated into the new Spektrum Pro Series Module and SR3500 Micro Receiver.

Jon Kerr—Team Schumacher USA Factory Driver

I first used one of the original M8 Spektrum module and receiver units in 2005 for the Reedy Race of Champions. I've had radio issues at the Tamiya America facility in the past, but this time I didn't have a single glitch all week. As a serious competitor, however, I could feel the slight latency in the system on the track and couldn't adapt my driving style to overcome it. Several months later, I returned to using crystals and my results improved once I did.

With these previous experiences, I was more than a little skeptical to try the Pro Series system when it was released. After talking to a number of other racers, I decided to give Spektrum a try again and I'm very glad I did. Now I feel no delays whatsoever when I am on track. If anything, my car feels more responsive than it did with crystals. I'm able to enjoy the benefits Spektrum offers and still be confident that I'm not going to have any radio issues. This is how radio systems should be made.

As a racer, I’ve been using the Spektrum system in competition for almost two years now and have never had an issue with my car feeling non-responsive. With the speed of today’s modified oval cars you need to feel connected every time you hit the track. The Spektrum system I use in combination with my JR Z-1 radio delivers the confident comfortable feel I’m looking for time after time.

As a race manager, the Spektrum system is one of the greatest innovations to come along in years. It simply speeds up the race program. Fewer frequency conflicts cause after qualifying re-sorts cause less time delays and help keep my race programs running smooth.

David Weir—2003 Tamiya Championship Series Mini National Champion

When I first read about the Spektrum system release, I was eager to give it a try, as it sounded almost too good to be true—no crystals and no conflicts to worry about. All of my expectations were met by the original Spektrum performance. No glitches, no conflicts, just walk right up to the drivers stand and turn it on. As I race primarily on carpet in a building with fluorescent lights, WiFi, and cordless phones, I was pleased to find virtually no problems. The sole issue I experienced on rare occasions was due to the ESD issue. Thankfully, the problem was quickly solved by the timely (and free) software update.

When the Spektrum Pro Series was announced, I was skeptical about the claims of reduced latency, but decided to give it a try. After a year of racing with the original Spektrum system, I had noticed just a slight latency in the system, something I only noticed "at the tone" start of the race. While some might say you shouldn't be able to tell the few microseconds difference, I immediately noticed that, with the Spektrum Pro Series equipment, I had a much more immediate response on the tone. Until I became accustomed to the faster response, I also found myself turning in just a touch early to each corner, but after just a couple of battery packs I adjusted to the faster response time.

As I love to race Tamiya Mini Coopers, I was also very impressed with the new SR3500 micro receiver—a true work of art. It is so small that I can now bury the micro receiver and my speed control down low and within the small confines of the mini chassis for a nice low center of gravity and neat appearance. The 2006 TCS Nationals had over 150 drivers participating, and it was a pleasure to never wait for a frequency clip, never have a glitch, and be fully confident of radio control of my car. I'll never go back to crystals again.

Rapid Response

As for my personal experience, I race at a variety of events from local club races, the US Touring Car Championships (The Novak Race), to the Tamiya Championship Series regional and national events. I started running the original Spektrum system during the summer of 2005, first in my Sportwerks Mayhem, then in my Tamiya TA-05. Now every car I own has Spektrum equipment.

I have attended the Tamiya Nationals every year since 1999 in Aliso Viejo, California at Tamiya’s headquarters. The track is known for having radio issues, and I have had glitching issues there in the past. The 2005 Nats was the first big race I ran a Spektrum system in and it was pretty sweet. I never had to wait for a frequency clip in all of practice, and I never had a single hit.

A few months later, I was able to test the Pro Series equipment in both my brushless and stock rubber Team Losi JRX-S cars at the 2006 Novak Race. I didn’t realize why at the time, but I kept turning in early for corners. It was the weirdest thing and I couldn’t figure it out until after the event. I had adjusted my driving style to drive around the latency without thinking about it, and one of the adjustments was to turn in earlier for corners and turn up my expo.

I have since adjusted to the faster response time and love my Pro Series equipment. I also like that I can still use my SR3000 receivers in my cars I just play around with, so I can still get use out of my original equipment. Oh, and at the 2006 Tamiya Nats, I also ran a Pro Series Module with the new SR3500 Micro Receiver. Again, I practiced when I wanted, never waited for a clip, and never had a radio hit. In fact, I never thought about my radio or frequency once all week. It was super dialed.

There can always be confusion, misconceptions, and otherwise bad information in the responses heard when a new technology is introduced. When it comes to Spektrum technology, Spektrum is a fluid sort of product and the development never ceases. A radio system’s speed and response time is all relative. With improved latency and a broad range of products available, there’s no good reason not to upgrade to Spektrum equipment. After all, the guy who just passed you probably did.